This invention relates generally to computed tomography (CT) imaging, and more particularly methods and apparatus for producing dynamically compensated CT images.
In at least one known computed tomography (CT) imaging system configuration, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the xe2x80x9cimaging planexe2x80x9d. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a xe2x80x9cviewxe2x80x9d. A xe2x80x9cscanxe2x80x9d of the object comprises a set of views made at different gantry angles, or view angles, during one revolution of the x-ray source and detector. In an axial scan, the projection data is processed to construct an image that corresponds to a two dimensional slice taken through the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered back projection technique. This process converts the attenuation measurements from a scan into integers called xe2x80x9cCT numbersxe2x80x9d or xe2x80x9cHounsfield unitsxe2x80x9d, which are used to control the brightness of a corresponding pixel on a cathode ray tube display.
Known CT imaging system scans include acquisition information and view information. xe2x80x9cAcquisition informationxe2x80x9d includes patient, scanning, and reconstruction information that is static in nature. xe2x80x9cView informationxe2x80x9d is actual attenuation data collected by a detection system of the CT imaging system and is dynamic in nature. In known CT imaging systems, compensation for dynamic changes from a patient or a scanning environment cannot be performed from present, view stream information alone. Thus, blurring in reconstructed images sometimes occurs. For example, images in fluoro CT applications are blurred during tilting of the gantry. Also, helical scans of different portions of a body using different helical pitches now require separate scans, because it is difficult to produce good images during speed transitions or even to compute actual image locations.
It would therefore be desirable to provide convenient methods and apparatus for compensating CT images for dynamic changes from a patient or scanning environment. It would further be desirable to provide such methods and apparatus for utilizing a view stream to provide the compensation information.
In one embodiment of the present invention, there is thus provided a method for imaging an object with a computed tomographic (CT) imaging system that includes steps of scanning an object with a beam of radiation from a CT imaging system to produce a view stream including attenuation data for the object being scanned; sensing one or more dynamic parameters relating to at least one of the object being scanned and the CT imaging system; and integrating information relating to the one or more sensed dynamic parameters into the view stream.
The above-described embodiment integrates information necessary for compensating reconstructed images directly into the view stream, thereby making the necessary information more conveniently available for such compensation.